In a balanced line interface, a pair of wires, i.e. lines A and B, is used to carry each datacom signal, and the data is encoded and decoded as a differential voltage between the two lines. A typical truth table for a balanced interface is as follows:VA−VB<−0.2v=0VA−VB>+0.2v=1
In principle, as a differential voltage, the balanced line interface is unaffected by differences in ground voltage between sender and receiver. Furthermore, if lines A and B are close together, they will be affected almost identically by external electromagnetic noise. If the lines A and B are also twisted together, e.g. a “twisted pair”, then neither line is permanently closer to a noise source than the other, which is extremely effective in eliminating noise from the signal.
V. 11 and V.35 are specifications which defines the connector type, the pin allocation and the signal level used for synchronous communications interfaces. The V.11 and V.35 specifications define differential interfaces for the clock and data signals, which are the only signals requiring high switching speeds for high-speed communications, e.g. up to 10 Mbps dependent on the equipment and cable used. However, 64 Kbps, 128 Kbps and 256 Kbps are other commonly used bit-rates. Separate clock lines are provided for receiving and transmitting data, and the remaining signals defined in the V.11 and V.35 specifications are unbalanced, i.e. single wire, and typically require minimal changes of state. Typical protocols used over V.11 and V.35 interfaces are HDLC, X.25, SNA and PPP.
A broken lead is the event when a datacom signal has high impedance or is open between the receiver and the external transmitter. A faulted lead is a condition when there is a fault in the differential pair between the receiver and transmitter such as a broken lead, low differential voltage, or a short.
An object of the present invention is to overcome the shortcomings of the prior art by providing a broken lead detector for a balanced datacom signal.